Thermo Top heat circuit

[BigSkyBrad]

Hi folks.

I'm at the point of installing the heating circuit. In my first camper(van) I had a Thermo Top with a calorifier on the main circuit, and a small fan matrix on an open-tee'd loop. For my current build, I want to expand on that, but still keep it 'basic' so that it's fixable in the field. I'm thinking of using simple ball valves so that I can isolate and balance. Ball valve no.1 is to prevent the header tank from being a heat-sink after bleeding. The tee valve is to bypass/reduce the calorifier once it is up to temp and not being drawn from. Later on, I thought I could add a heat exchanger and pump to join the engine heat into it, or have another Thermo Top for the engine (that way I have a spare on board).

(see diagram) Feel free to comment, spot faults or limitations, improvements - any thoughts appreciated.

 

[gait]

silly question - how will you know when the calorifier is up to temperature? (Hint - I have a temperature sensor on the hot out with copper connection but its still low until I run some water).

the ThermoTop stops heating around 76 deg C, which would also then be the max temperature it could heat the calorifier to.

nice trick with the header tank flexibility. Most times in Aus its useful to lose some heat.

 

[BigSkyBrad]

Temp gauge on the callorifier outlet is a good idea. With our previous camper, I knew it took about 15-20 mins to heat the 20l calorifier. This time we're having 30l, so it will take a little longer. Even with the extra radiator lines, the calorifier is the Webasto's first port of call until it's shut off or reduced.

 

[SkiFreak]

One of the challenges with hydronic systems is knowing where you have flow and where you don't. Generally, fluid will take the path of least resistance, so working out how much a valve should be open or closed can be a bit of hit and miss when trying to "balance" the system. Closing one valve completely can also affect that balance.
Adding some method of monitoring flow, like visual flow indicators or hall sensors, can definitely help, but finding units that will handle 80 degree Celsius temperatures can be a challenge.

The other thing to remember when using something like the ThermoTop boiler is that it works most efficiently if it is not cycling on and off. You will also get far less carbon caking of the burner if it runs continually.
In order to make this happen, sometimes it is necessary to design an inefficient heating system, where heat is intentionally lost. By doing this it keeps the coolant temperature below the thermostatic cutoff temperature of the ThermoTop.

So, as much as your idea of isolating the calorifier after it has heated the water may seem like a good idea, it may actually work against you when it comes to system efficiency.

 

[BigSkyBrad]

So, as much as your idea of isolating the calorifier after it has heated the water may seem like a good idea, it may actually work against you when it comes to system efficiency.

So, I shouldn't bypass the header tank too - ie. keep that flowing through fulltime? I did have it fulltime flowing on the previous build, but it seemed a waste of heat.

 

[SkiFreak]

In most hydronic systems you aim for as much thermal efficiency as possible, but using a ThemoTop boiler for hydronic heating is a different scenario, as it was never really designed for this function.

I did have it fulltime flowing on the previous build, but it seemed a waste of heat.

As I mentioned, having the ThermoTop running without cycling is ideal, so you should bleed off as much heat as necessary to achieve that goal.

 

[BigSkyBrad]

I have the opportunity to buy a new Thermo Top Evo-5 at a cracker price, but it is a specific one for a VW/Audi. I read somewhere that they only run for an hour then shut down. The refurbished ‘C’ in my previous build (LT35) may have been the same but I only ran it for the 20mins to heat the calorifier, and only ever ran it for space heating for about 20 mins at a time so never struck the issue. But this new build, with a bigger space to heat, and a lot more time spent in it and in different climates, the heater will need to run longer, even through the night on occasion.

So my question is, can they be tweeked/wired to run longer like a marine/narrowboat/RV universal one, both manually and/or temp-time controller?

 

[Alloy]

A heat loss calc will tell how many Kw or BTU is needed and indicate how much needs to be lost to balance the start/stop cycles

Home Heat Loss Calculator

Stick and Brick hydronic equipment is time tested so reliability isn't a reason to not use it.

You don't want the floor loop hotter than say 50C and same goes for the towel bar. A towel bar at 76C will burn.

Truma (gas) Combi might be an option

Truma heaters for caravans and motor homes

Truma has been developing and producing heaters for caravans and motor homes for more than 60 years. Find out more about the various models.

www.truma.com

 

[Joe917]

I would let the coolant through the calorifier always and stay connected to the header tank always.
As for a heat exchanger to the engine just plumb it in its designed to run engine coolant. put a ball valve on both connections for emergency shut off. leave one open all the time and use the other to open or close the connection.
This set up has run like this on our truck for 25 years.

 

[BigSkyBrad]

I had used a Surecal 22l calorifier in the first build and was happy with the quality, so am using their vertical 30l this times - thinking on it, for the extra £25, I should get the twin-coil model for the engine hook-up.

I read somewhere on here, someone said the system should be a higher kw output than the diesel heater's output for it to be efficient and minimal short cycling(?). The heater is 5-5.5kw - the towel rail is 175, the rad is 490, and I doubt the floor loop and calorifier make up the rest. Just a quick poke around found a super-quiet (46db) fan matrix putting out 5.5kw, 15mm copper matrix and connections, the fans draw 2amp max, and is a size that I squeeze it in somewhere.

Quiet Car Heater 320mm

QUIET HEATER Yes - only 46db noise output - you can hardly hear it. Requires hot water feed from your engine. Supplied as shown below so it's ideal for maybe a secondary heater in the back of a limo, van or motorhome. 12½" (320mm) wide x 6" (152mm) high x 5" (125mm) front to back. Heat output...

www.carbuilder.com

I'm guessing the more heat I can output is directly proportional to how happy the wife is!

 

[gait]

the valved by-pass across the header tank is very useful. It really depends where you are and where you travel. In some climates its useful to bleed heat so the unit doesn't cycle - at one stage I had a fan driven radiator outside. I have a well insulated solid box not a fabric pop-top and no gas so no gas vents, just windows to open. In other climates all the heat is needed inside. Its also seasonal.

I also have the diesel heater plumbed directly into the engine. Two ball valves (motorised) with switches inside to isolate engine and/or diesel heater. 10 years and still ok. Third manual ball valve so if something in heater circuit leaks I can isolate the engine. I also carry a couple of short bits of copper pipe to separate engine and heater completely should the need arise due to failure of something.

46dB is IMHO not quiet. I continue my search for less than 25dB. My current fans are variable speed (continuous not on/off) but still have some bearing noise. Its hard to find quiet small high flow fans. A few years since I looked. Variable speed fans also help with temperature control inside. Ten years ago I was also concerned about energy use. Now solar is relatively cheap.

12 year old thermotop E cycles every hour. I bypassed the complicated digital control with a single on/off switch (across red/black wires). The timer is in the heater itself not the remote controller (which has additional timer ....).

In use, we don't leave the heater on overnight, apart from a couple of times in -10 deg C. Having lots of heat available for quick start in the morning - fans on full, water directed to fan heaters. Evening the requirement is for constant heat, the internal fittings are all warm, a very different level of comfort (its not just temperature). Its also nice at the end of a drive in cold weather to have had engine heating rear, usually have to open windows as everything is "soaked" warm (and cosy).

Depends where you are travelling. My E has automatic altitude compensation - it worked fine at 5,000 metres. I don't know about other/current models.

 

[BigSkyBrad]

@gait We live in Scotland which is not the warmest, and given the coronavirus borders loosening up, Europe can be just as chilly if you travel in the wrong direction.

My previous one had one of those cheap chinese timers, but I always used the manual mode as I couldn't fathom the chinglish instructions for the timer!

 

[Joe917]

The Heatmiser 12 volt thermostat works flawlessly with the Thermotop C. Set Temp and enjoy!

 

[SkiFreak]

So my question is, can they be tweeked/wired to run longer like a marine/narrowboat/RV universal one, both manually and/or temp-time controller?

The articles I wrote on my website may be of use to you...
Wiring up a Webasto Thermo Top C
Heating – Water & Camper

 

[BigSkyBrad]

@SkiFreak When i bought my previous (refurbed) Webasto, it came with a full loom with the chinese timer already joined in. I vaguely remember using your wiring article to cut out the excess from the loom!